I. Field
The present disclosure relates generally to electronics circuits, and more specifically to delay circuits.
II. Background
Synchronous circuits are circuits whose operation can be controlled by control signals such as clock signals, strobe signals, enable signals, etc. Synchronous circuits are in contrast to combinatorial circuits that can change their outputs whenever their inputs change. Some examples of synchronous circuits include latches and flip-flops, which may be operated in a synchronized manner based on a common clock signal.
Synchronous circuits such as latches and flip-flops are widely used in various digital circuit designs. A latch is a circuit that can store one bit of information and can be controlled by a control signal such as a clock signal. A flip-flop is a circuit that can store one bit of information and can capture input data based on clock edges. A main difference between a latch and a flip-flop is transparency, which relates to how data is captured and maintained. For a latch, the output may follow the input when the control signal is at high logic, an input data value may be captured when the control signal transitions to logic low, and the captured value may be retained while the control signal is at logic low. For a flip-flop, an input data value may be captured at one edge (e.g., rising edge) of the clock signal, and the captured value may be provided to the output at the other edge (e.g., falling edge) of the clock signal. Hence, the output of the flip-flop is non-transparent to the input. The terms “latch” and “flip-flop” are often used interchangeably when the distinction between their manners of operation is not important. Multiple flip-flops may be coupled in parallel or in series to form a register for any number of bits.
Synchronous circuits have certain propagation delays between their inputs and outputs. The propagation delays may be due to logic gates used to implement the synchronous circuits and may vary widely due to variations in integrated circuit (IC) process, power supply voltage, and temperature (PVT). When synchronous circuits are used in high-speed digital circuits, it may be desirable or necessary to account for the propagation delays of the synchronous circuits across PVT variations in order to support high operating speed and achieve good timing margins.